This is the method of encoding and decoding the video and audio compression. There are many systems in use, each offering advantages and disadvantages. The RealPlayer codec enable video clips to be sent down a telephone line. The quality is porr, small images and whooshy audio, but it works at the level intended. Video which is digitised at 24 bits per pixel, 720 x 576 pixels per frame, 25 frames per second needs a bandwidth of about 250 Mbps or 80 MBps. A simple compression reduces this to just under 4MBps for storage on digital video tape.